The present invention relates to sheet-fed scanners, and in particular to scanners connected by a peripheral bus to a host computer.
A typical sheet-fed scanner includes a roller, or platen, with a resilient, high friction material on the outside of the platen. The platen is rotated by a motor to draw paper into the scanner. The paper is typically moved between the roller and a contact image sensor (CIS). The contact image sensor will typically have a line of LEDs, with different color LEDs for a color scanner. Alternately, fewer or one LED could be used, with an optical element spreading the light to all the pixel positions of a line.
Such a scanner can either connect to a peripheral bus of a host computer, or could be embedded in a computer, such as being embedded in a laptop. A separate power cord will connect to line power or to the computer's line power in the laptop for providing the power needed to drive the scanner's motor, CIS sensor, and other electronics.
A number of other different types of peripheral devices connect to a computer. For example, mice, joysticks, trackballs, touchpads, etc. can be connected to the peripheral port of a computer or embedded in a laptop. For devices which are separate and connect to peripheral port, it is desirable to be able to obtain power over the peripheral bus, rather than requiring a separate power cord. Some devices which use low amounts of power, such as a mouse, can do this. The recently developed universal serial bus (USB), for instance, provides four connectors, two for data and two for power and ground. Power can be obtained from the host computer's 5 volt supply (which is actually 4.5-5.5 volts). However, only 2.2 watts of power are available. A typical scanner, due to the high power requirements of the motor for the platen, and the power requirements of the CIS scanner, typically requires in the neighborhood of 12 watts of power, an order of magnitude higher than the power available over the USB.